Along with the development of the display technology, because the liquid crystal display device has advantages of small size, low power consumption and so on such that the liquid crystal display device is favored by many users. The liquid crystal display device generally includes a circuit board, a backlight module and a liquid crystal panel. The circuit board is used for driving the backlight module and the liquid crystal panel. The backlight module is used for providing light to the liquid crystal panel. The liquid crystal display panel is used for displaying information of text, picture, etc. the circuit board usually includes a direct-current voltage conversion circuit in order to convert a received first direct-current voltage to a second direct-current voltage, and outputting the second direct0current voltage. Wherein, the first direct-current voltage is not equal to the second direct-current voltage. When the first direct-current voltage is greater than the second direct-current voltage, the direct-current voltage conversion circuit is a buck circuit. When the first direct-current voltage is less than the second direct-current voltage, the direct-current voltage conversion circuit is a boost circuit. However, the voltage conversion circuit in the conventional art does not include an abnormal (for example, the voltage conversion circuit is short with respect to a ground) detection circuit. When the voltage conversion circuit generates an abnormality, the current passing through the electric elements in the voltage conversion circuit will exceed a preset current (such as a rated operating current) so that the electric elements in the voltage conversion circuit are burned.